The IP Multimedia Subsystem (IMS), defined in Release 5 standards of the 3rd Generation Partnership Project, is a subsystem that supports IP multimedia services. The IMS uses the Session Initiation Protocol (SIP) call control mechanism to create, manage, and terminate various types of multimedia services. The IMS provides a basis for service convergence. Based on IP technologies, the IMS supports voice, data and multimedia services as well as new applications.
The IMS MRBT service is a service which is effective when its subscriber is called. When a call is originated via the IMS domain and the callee is able to answer the call, if the callee is an MRBT service subscriber and has ordered a tone, the ordered tone, such as an audio, video or other multimedia file, will be played to the caller instead of an ordinary ring back tone when the caller waits for the callee to answer the call.
FIG. 1 shows a flowchart of call termination by an IMS MRBT service subscriber.
Step 101: A caller originates an IMS call request.
Step 102: The called Call Session Control Function server (CSCF) receives the IMS call and determines whether the callee has subscribed to the MRBT service according to the service profile of the callee stored in the Home Subscriber Server (HSS) of the callee.
Step 103: If the callee has not subscribed to the MRBT service, the called CSCF sends an IMS call signaling message to the callee.
Step 104: If the callee has subscribed to the MRBT service, the called CSCF sends the call signaling message to the callee tone Application Server (AS).
Step 105: The callee tone AS starts media negotiation between the caller and the called Media Resource Server (MRS) and sends a call signaling message to the callee via the CSCF.
Step 106: The callee tone AS instructs the called MRS to play a tone to the caller when the callee is alerted.
With the above solution, an IMS MRBT can be played to a caller but the played MRBT is ordered by the callee. The solution provides personalized services for the callee. The inventor, however, has not found any ring back tone service ordered by a caller to reflect the personal liking of the caller or any solution that determines whether to play the ring back tone ordered by the caller (referred to as “caller tone”) or the ring back tone ordered by the callee (referred to as “callee tone”) to the caller when the caller and the caller are both MRBT service subscribers.